**5. Quality and postharvest**

The quality of a product encompasses sensory attributes, nutritional value, chemical constituents, textural properties, functional properties, and defects [58]. Consumers use their five senses - sight (appearance), smell (aroma), taste, touch (texture) and hearing to evaluate the product quality, and integrate all these senses to decide on the acceptability of the product [58].

In the specific case of consumer acceptability and quality evaluation of table grapes different attributes must be considered, which are reached in the third and last stage of berry development, and includes intrinsic (visual, mechanical, chemical, etc) and extrinsic (cultivar, production methods, country of origin, price, etc) attributes [59].

Visual characteristics and physicochemical properties are involved in sensory and quality evaluation of table grapes. The color, size and shape of the berry are the primary characteristics that consumers observe, together with taste, aroma, and texture [59, 64]. Consumers favor freshly picked, moderately dense triangular bunches, with a fresh, green-colored rachis. They also prefer grapes with juicy, firm flesh and few or no seeds [45, 59].

The firmness of grape berries is a quality parameter widely associated with the characteristic of crunchiness, and indicates that they have been recently harvested [54]. Loss of firmness is associated with loss of turgidity and physiological modifications that affect berry structure [54, 56].

The harvest date of table grapes is set by the producer taking into account the following quality parameters: SSC, TA, SSC/TA ratio and color [59].

Table grapes are considered non-climacteric fruits with a relatively low rate of physiological activity that exhibits a gradual decrease in respiration during ripening [65]. The berries exhibit very low ethylene production and low respiratory intensity, while the respiratory intensity of the rachis is 15 times higher than that of the berries [45]. Therefore, the quality of table grapes tends to deteriorate rapidly during postharvest, reducing its shelf-life.

Table grapes are subject to severe postharvest losses during the storage and long-distance transport, being mainly of physiological, mechanical, and microbial infection origin [66]. During postharvest, table grapes are sensitive to rapid moisture loss, which results in rachis drying and browning, water loss, berry shatter, and fungal infections (mainly caused by *Botrytis cinerea* Pers. and *Penicilium* spp.), the most important factors limiting their quality and marketability and causing quantitative and quality losses [40, 59, 66]. This type of disorder often occurs due to improper handling during harvest, and throughout the marketing process. However, this characteristic is very distinct among varieties, in some cases being an obstacle to its commercialization over long distances, as is the case of the 'Dona Maria' Portuguese variety. Temperature and humidity control, as well as improved packaging conditions can reduce the undesirable occurrence of fungi.

It is generally agreed that the most important and destructive postharvest disease in table grapes is gray rot, caused by the fungus *Botrytis cinerea* Pers. [45, 47]. Gray rot can originate from latent infections initiated before harvest, from spores present on the bunch, and from visibly infected berries that have not been eliminated during selection operations [47]. These, which at the beginning have a white coloration, after a few days acquire a grayish coloration, which characterizes the disease (**Figure 5**) [47].

Another disease that occurs during the postharvest period is blue rot caused by fungi of the genus *Penicillium* spp., which although less important than the one mentioned above, also causes damage during the storage period of table grapes (**Figure 6**).

*Table Grapes: There Is More to Vitiviniculture than Wine… DOI: http://dx.doi.org/10.5772/intechopen.99986*

#### **Figure 5.**

*Magnifying glass observation of Botrytis cinerea on a 'Crimson' table grape berry using an Olympus SZ61 at 350X magnification.*

#### **Figure 6.**

*Magnifying glass observation of Penicillium spp. on a 'Crimson' table grape berry using an Olympus SZ61 at 350X magnification.*

The contact of infected fruit with healthy fruit, leads to its contamination, so that through the existence of an inoculum in a berry, it easily spreads throughout the cluster [47]. The infection can be initiated in the vineyard, in the packaging units or during the storage period.

The most commonly applied postharvest techniques are based on the optimization of temperature and control of the relative humidity of surrounding atmosphere, as well as the development of packaging, which limits the decrease in moisture content and protects against physical damage during the entire postharvest period.

Temperatures between −1 and 1°C and 90 to 95% relative humidity are established as assertive conditions for table grapes [45, 47]. Refrigeration, associated with high relative humidity, is one of the most appropriate technologies to extend the shelf-life of fruits, since low temperatures decrease biochemical reactions, microbial activity and minimize moisture loss by reducing transpiration [67].

The commercially recommended method for table grape preservation consists of rapid pre-cooling immediately after harvest followed by sulfur dioxide (SO2) spraying, keeping the temperature and relative humidity at these values constantly throughout the storage period, which will decrease the losses associated with this period [47]. The use of sodium metabisulfite generators is another of the table grape preservation practices commonly used in the international market, in the form of papers impregnated with the active substance, or bags with the solution or powder formulation, considering the higher the temperature and relative humidity, the faster the gas is generated [47].

Modified atmosphere packaging (MAP), associated with refrigeration, has beneficial effects in preventing weight loss, reducing metabolic activity, decreasing color changes in the berry and rachis, reducing respiration rate, decreasing microbial populations with consequent reduction of fungal incidence over shelf-life [68, 69]. Moreover, several studies have referred the use of MAP in table grapes, with perforated and non-perforated plastic films, based especially on polyethylene and polypropylene [69].

The use of controlled atmospheres (CA) is another technique used to maintain quality attributes and control postharvest losses in table grapes.

In addition to the techniques presented, it is also possible to mention the use of ultraviolet radiation (UV-C) [70], hypobaric and hyperbaric treatments [71] and treatments with gaseous ozone, ozone in water or ozone injection in the cooling chambers [72–74].

Therefore, it remains necessary to develop strategic, residue-free alternatives for postharvest quality control of table grapes that are safe for health and the environment and compatible with commercial practices.

In recent years, there has been a growing interest in the use of innovative and environmentally friendly technologies, such as edible coatings or films and biodegradable films associated with the application of natural compounds, like essential oils, that will both add value to food products and extend their shelf-life [75–77].

#### **6. Nutritional value of table grapes**

The nutritional and functional interest of grapes in the human diet makes relevant the knowledge of its chemical composition, which is very complex. Although there are differences in the chemical level for different varieties, agronomic aspects, and locations. The chemical composition of grapes (European type, such as 'Thompson seedless'), red or green, raw, is presented below in a generic way, according to the USDA *FoodData Central* (**Table 1**) [78].

In general, table grapes, like other fruits, have a high-water content, close to 80%, provide carbohydrates, mainly in the form of sugars, and are low in proteins and lipids. It also noteworthy the large quantity and diversity of vitamins, essential amino acids, and minerals, with a high potassium content.

It should also be noted that grapes are rich in different polyphenols (phytochemicals which are antioxidant compounds), which contribute to physiological and biological activity for the food industry such as antioxidant and antimicrobial activities [79, 80].

Resveratrol is a phenolic compound with antioxidant activity, present in berry skin of grapes. Analyses with 'Dona Maria' grapes revealed that this variety has high concentrations of this compound [28].

In recent years, there has been a notable increase in the interest for grape byproducts, such as seeds and skins, which have nutritional properties and biological potential with nutritional and pharmaceutical application, such as anticancer, anti-inflammatory, cardiovascular prevention [79, 81, 82].

*Table Grapes: There Is More to Vitiviniculture than Wine… DOI: http://dx.doi.org/10.5772/intechopen.99986*


**Table 1.**

*Chemical composition of table grapes. Nutritional information about energy value of the grape per 100 grams of fresh weight for organic constituents; per 100 g of dry weight for minerals [78].*
